Entering Under initially feels like going into a sauna, as wooden planks cover its upper section, but an eight-metre flight of stairs leads down to a large dining area that sits about 40 guests, walled by a gigantic transparent window to the ocean.
Traedal Thorsen said the construction can cope with very harsh weather and is shaped in such a way that it can withstand what he called "the wave of the century".
The restaurant is laid out so there are minimal reflections in the glass wall, which fills the room with natural light during the day, filtered by the greenish colour of the water.
A full 18-course meal, based on local ingredients and seafood, can cost up to 3,700 crowns ($430) per person including drinks.
"The goal is to get 50 percent of the guests who eat there to spend the night in the hotel as well... We expect around 12,000 people eating dinner every year.